Injection pump



Patented Aug. 17, 1937 UNlTED TSTATES PATENT OFFICE" Willy Voit, Stuttgart-Bad Cannstatt, Germany, assignors to Robert Bosch Aktiengesellschaft,

Stuttgart, Germany Application July 3, 1935, Serial No. 29,702 In Germany July 20, 1934 Claims.

In engines to which fuel is supplied by injection pumps, there is usually a drawback that the amount of fuel delivered when under full load does not accord at all speeds with the fuel re- 5 quirement necessary to obtain a satisfactory combustion. In general, the amount of air induced at each stroke diminishes as the speed increases, and the amount of fuel supplied to the cylinders during maximum outputmust therefore be so proportional that it corresponds at a certain speed to the reduced degree of admission. As however,

- the injection pumps at all speeds deliver prac-, tically uniform amounts of fuel, which often even increase as the speed increases, a reduction in output occurs at low speeds such as for example, in the engines of vehicles ascending an inclined, as the larger amount of fuel corresponding to the required increased degree of admission is then no longer supplied to the cylinders. I

When the pumps have a suction passage controlled by a slide-valve, the amount of fuel delivered is larger, particularly as the speed increases. At a high speed of the delivery piston, owing to, the throttling action which takes place in the movement of the particles of fuel, the delivery operation commences before the controlling edge of the piston has completely closed the suction passage; on the other hand, at low piston speed the delivery operation begins only when the suction passage is almost fully closed.

The present invention has for its object to adapt the amount of fuel delivered when under full load to the fuel requirement of the engine, without additional controlling devices dependent on the speed. 'The invention consists in the pressure-valve being of a form which gives a substantial cross sectional passage for fuel only after a large stroke, for the purpose of producing a return-flow of fuel from the pressure pipe, which 40 increases as the speed rises, so that the pressure valve must make a considerably larger stroke at a high speed than at a low speed, at which only small cross sectional areas of passage are necessary and the valve stroke is consequently less. On the closing movement initiated after the conclusion of the delivery stroke, for example, by the controlling of the return-flow passage, it is impossible for fuel to reach the pressure pipe, owing 0 to the passage cross-section quickly becoming narrower. The volume of the pressure pipe is thus increased by the volume of the stroke which the valve bodyfrees during the closing movement. The valve body thus acts like the wellknown relief-piston, but is distinguished from this latter very essentially by the fact that the relief volume is substantially larger at high speeds than at low speeds. When the relief of the pressure spaces is great owing to high speeds, more fuel is required on the next delivery stroke for filling the pressure spaces, and therefore only a smaller part of the total amount of fuel delivered to the pressure pipe emerges from the injection nozzles into the cylinders of -the engine than on the smaller relief which occurs as a consequence of the smaller delivery speed.

In the drawing, Fig. 1 is a diagram representing the fuel requirement of different engines.

Fig. 2 is a corresponding diagram, which shows the amounts of fuel delivered by the injection pumps independence on the speed. Fig. 3 is a section through one form of construction of the I invention.

The lines A, B and C in Fig. l are graphs representing the fuel requirement in dependence on the speed of different engines at maximum output. The abscissa 111 represents the lowest driving speed of about 400- per minute, while the abscissa n: represents the highest driving speed of about 2,000 per minute. The fuel requirement of many engines is in accordance with the graphs A, while other types, owing to more favourable eddy action of the air admission at high speeds have a characteristic curve in accordance with B or even C.

The conditions are the reverse in injection pumps, whose delivery curves are represented by the graphs in Fig. 2. Owing to the increased gap action at high. speeds, slide-valve controlled pumps show a curve C1, in'valve pumps the delivery remains almost equal as in curve B1 at all speeds, whilst the characteristic curve A1 desirable for engines having the curve A in Fig. 1 can hitherto only be obtained by inconvenient mechanical supplementary governors working in dependence on the speed. If an injection pump working according to the curve C1 is to be employed for an engine with the curve A without this supplementary governor, the amount delivered must be throttled to a smaller amount 00116'. sponding to the ordinate above 122 up to the point of intersection with the curve A in Fig. 1. If, now, one inserts in Fig. 1, starting from this point of intersection, the curve C1 corresponding to the line C1 in Fig. 2, as indicated in broken lines, this intersects the ordinate above 111 at the point P; the output thus sinks at a low speed by a considerable amount corresponding to the delivery reduced by the distance m.

The invention enables an injection pump, itself delivering according to curve 01, to be given, without additional governing devices, a delivery characteristic A1 perfectly corresponding to the requirement curve A.-

5 For this purpose, according to Fig. 3, a valvebody 8, loaded by a spring 1 and provided with a closing part 5, is fitted in front of the pressurepipe 6 leading to the injection nozzle (not shown). The valve-body is provided with con- 10 trolling grooves 9, which gradually diminish 'in depth adjacent to and toward their upper ends, said valve body cooperating with the controlling edges II formed on the casing Ill. The injection pump consists essentially of a delivery piston l2 15 mounted so as to be longitudinally movable in a casing I3, said piston co-operating with a suction passage I4. A return-flow passage I5 is controlled by an inclined face formed on the piston I2. A delivery chamber I I5 is provided 20 above the piston I 2.

The mode of working of the arrangement is as follows:--

1 By the controlling grooves 9, which strongly throttle the cross-section of the passage on a 5 small stroke of the piston, and only constantly increase after'a large stroke, the result is obtained that at a high delivery speed a substantially larger part of the valve-body 8 is raised from the guide II than at low delivery speed. 30 Let it now be assumed that the piston I2 has finished its effective delivery stroke. This is the case as soon as the oblique controlling edge 28 begins to control the return-flow passage I5 on the delivery stroke, so that the largest part of 35 the fuel forced out of the pump chamber I8 on the further stroke can escape through a longitudinal groove 2| in the controlling face of the pump piston I2 through the return-flow passage I5 now opened by the controlling edge 20. A 40 pressure difference is then created between the fluid-chambers I 6 and I1 bounded by the controlling body 8, under the influence of which the controlling body 8, assisted by the force of the spring 1, is moved towards the end-position indi- 45 cated in the drawing. Accordingly, the flow of fuel ceases, owing to the rapidly increasing throttling action of the controlling grooves 9 again narrowing the passage cross-section, for this throttle action is stronger than the resistance 50 to fiow still existing shortly after the controlling of the return-flow passage I5 between itsmouth and the controlling edge 20. As thus no further fuel can reach the pressure-pipe Ii, the capacity of the pressure-pipe is increased during the fur- 55 then closing movement of the valve-body 8 by the stroke volume or capacity which the valvebody gives after the conclusion of the delivery operation until the closing member'5 comes on to its seat. This stroke volume is dependent on 60 the speed; at high speeds it is larger than at low speeds. On the succeeding delivery stroke, the volume represented by this stroke must now be again filled up before fuel can emerge from the nozzle. At high delivery speeds, however, the .5 amount of fuel required for filling the pressure -spa'ces I1 and 8 -is greater, therefore only a smaller part of the total amount of fuel delivered into these spaces can emerge from the noz- 'zle into the cylinder or cylinders of the engine than at the low delivery speeds corresponding to a low engine, speed, in which the stroke volume released by the valve-body 8 during its closing movement is far smaller. In order, even at a low speed, to relieve the pressure-pipe 6 to such an extent after the conclusion ,of the delivery stroke that fuel can no longer drop at the nozzle, the valve-body 8 is provided with a piston-like part I8 which'completely shuts off the passage crosssection at the controlling edge II towards the end of the closing movement.

In the fuel path between the seat of the closing member and the controlling edges II an equalizing chamber IS in the form of a cross-sectional enlargement is introduced, which, it has been ascertained, assists the relief action of the valve. By suitably proportioning the force of the spring 1, and/or by a stop adjustable if required, to limit the opening movement of the valve-body 8, as well as by the form and number of the controlling grooves 9, the delivery curve of the pump can be adapted within wide limits to the fuel consumption of the engine. The size of the valvebody must, of course, be suited to the deliveryvolume of the pumps; the most favourable conditions are obtained if the diameter of the valvebody 8 is about equal to that of the delivery piston I2. For certain constructional conditions, more especially for the subsequent installation of the apparatus in an existing plant, it may be preferable to construct the casing III of the valvebody 8 as a constructional part introduced separately from the injection pump and its pressurevalve in the pressure-pipe 6.

We declare that what we claim is:

1. An injection pump comprising a pump body, an injection nozzle, a piston reciprocable within said body, a pair of ports, one of which is an inlet to the pump and the other functions as a port for the return passage of fuel, controlled by said piston, a valve seating on said body, a pressure conduit. leading from said piston to said nozzle, a loaded valve displaceable relatively to said seating under the action of said piston, and controlling the flow of fuel to said pressure conduit, the cross-sectional area. of said valve remote from the piston and the end engaging on the seating being such as to completely close said conduit when the valve is on its seat, the crosssectional area of the remainder of said valve being less than at said remote end and gradually diminishing intermediate said remote and seating ends and toward the seating end whereby after said valve has opened to a predetermined degree a throttling passage for flow of fuel is provided which gradually increases in cross-section with further opening of said valve.

2. An injection pumpcomprising a pump body,

van injection nozzle, a piston reciprocable within said body, a pair of ports, one of which is an inlet to the pump andthe other functions as a port for the return passage of fuel, controlled by said piston, a valve seating s-qn said body, a pressure conduit leading from said piston to said nozzle, a loaded valve displaceable relatively to said seating under the action of said piston, and

controlling the flow of fuel to said pressure conduit, the cross-sectional area of said valve re-' mote from the piston and the end engaging on the seating being such as to completely close said 'conduit when the valveis on itsseat, grooves being formed in the remainder of the valve between the seat and the remote end to forms throttle for the passage of fuel past the valve after said valve has opened to a predetermined degree, said grooves gradually diminishing in depth adjacent to and toward said remote end whereby said throttle passage gradually increases in' cross-section with the further opening of said valve.

3. An injection pump comprisinga pump body,

an injection nozzle, a piston reciprocable within said body, a pair of ports, one of which is an inlet to the pump and the other functions as a port for the return passage of fuel, controlled by said piston, a valve seating on said body,1a pressure conduit leading from said piston to said nozzle, a loaded valve displaceable relatively to said seating under the action of said piston, and controlling the flow of fuel to said pressure conduit, the crosssectional area of said valve remote from the piston and the end engaging on the seating being such as to completely close said conduit when the valve is on its seat, grooves being formed in the remainder of the valve between the seat and the remote end to form a throttle for the passage of fuel past the valve after said valve has opened to a predetermined degree, said grooves gradually diminishing in depth adjacent to and toward said remote end whereby said throttle passage gradually increases in cross-section with the further opening of said valve, and an equalizing chamber formed in the pump body on the discharge side of the valve seat to increase the cross-sectional area of the fuel passageway immediately in rear of the seat.

4. An injection pump comprising a pump body,

an injection nozzle, a piston re :iprocable' within said body, a pair of ports, one of which is an inlet to the pump and the other functions as a port for the return passage of fuel, controlled by said piston, a valve seating on said body, a pressure conduit leading from said piston to said nozzle, a loaded valve displaceable relatively to said seating under the action of said piston, and controlling the flow of fuel to said pressure conduit, the

cross-sectional area. of said valve remote from the piston and the end engaging on the seating being substantially equal to that of the crosssection of the piston and such as to completely close said conduit when the valve is on its seat, the cross-sectional area of the remainder of said valve being less than at said remote end and gradually diminishing intermediate said remote and seating ends and toward the seating end whereby after said valve has opened to a predetermined degre'ea throttling passage for flow of fuel is provided which gradually increases in cross-section with further opening of said valve. 5. A fuel injection pump for supplyingfuel to engines, comprising a cylinder, a reciprocable piston mounted therein, a discharge valve, a pressure conduit behind said valve, and means for releasing an adjustable amount-of the fuel displaced by said piston at its pressure stroke, said discharge valve being so formed that it opens with increasing opening stroke a throttle passage of increasing cross-sectional area for flow of fuel so that the cross-sectional area of the passage offered to the back flow of fuel from said pressure conduit to the piston after the releasing, and therewith the amount of fuel delivered at the following pressure stroke of the piston, depends on the lift of said valve, which lift is considerably larger at high speeds than at low speeds of the engine.

HANS HEINRICH.

MAX HURST.

WILLY VOIT. 

